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Free Space Optics (FSO) A Technical Paper on Free Space Optics The Technology at the Heart of Optical Wireless ABSTRACT Free-space optical communication systems can provide high-speed, improved capacity, cost effective and easy to deploy wireless networks. Experimental investigation on the next generation free-space optical (FSO) communication system utilizing seamless connection of free-space and optical fiber links is presented.The technology is useful where the physical connection of the transmit and receive locations is difficult, for example in cities where the laying of fibre optic cables is expensive and in establishing MANs where a single feet can be the most daunting. Free Space Optics (FSO) is far more secure than RF or other wireless-based transmission technologies. The only essential requirement for Free Space Optics (FSO) or optical wireless transmission is line of sight between the two ends of the link.Also presented various applications of FSO in Defense ,Network Solutions and in many General Purposes.The reliability of an FSO link can be increased by using various techniques. The challenges in establishing a FSO link are fog , the case when the optical signal hits a target and the case of interrupting signals and their remidies are also explained. Companies and rapidly advancing FSO technology are brought in detailed Free Space Optics (FSO) CONTENTS Introduction Why choose this topic? What is Free Space Optics (FSO)? Free Space optics (FSO): An Introduction History WORKING PRINCIPLE OF FSO FSO: Wireless, at the Speed of Light How Free Space Optics (FSO) can help us Advantages of Free Space Optics (FSO) : Free Space Optics (FSO) Security Military Application of FSO FSO vs RF Reliability of the FSO link Challenge of FSO Challenge #1 — FOG Challenge #2—hitting the target Challenge #3—interrupted signals Companies and rapidly advancing FSO technology AirFiber Free Space Optics (FSO) LightPointe Terabeam General Applications Conlusion References Free Space optics (FSO): An Introduction In telecommunication, Free Space Optics (FSO) is an optical communication technology that uses light propagating in free space to transmit data between two points. The technology is useful where the physical connection of the transmit and receive locations is difficult, for example in cities where the laying of fibre optic cables is expensive. Free Space Optics is also used to communicate between space-craft, since outside of the atmosphere there is little to distort the signal. The optical links usually use infrared laser light, although low-data-rate communication over short distances is possible using LEDs. IrDA is a very simple form of free-space optical communications. Distances up to the order of 10 km are possible, but the distance and data rate of connection is highly dependent on atmospheric conditionsInformation Age. Free-space optics (FSO), also called free-space photonics (FSP), refers to the transmission of modulated visible or infrared ( IR ) beams through the atmosphere to obtain broadband communications. Most frequently, laser beams are used, although non-lasing sources such as light-emitting diodes ( LED s) or IR- emitting diodes (IREDs) will serve the purpose. Free Space Optics (FSO) Why to choose this topic? September 11, 2001, New York Every thing was destroyed including normal fiber link Wall street stock market was closed because the communication was destroyed Two of these units were used between building to re-establish a high speed communication link Free Space Optics (FSO) FSO communication between Merrill Lynch Brokerage and Wall Street in New York following the terrorist attack that destroyed normal fiber optic link What is Free Space Optics (FSO)? Free Space Optics (FSO) or Optical Wireless, refers to the transmission of modulated visible or infrared (IR) beams through the air to obtain optical communications. Like fiber, Free Space Optics (FSO) usesLasers to transmit data, but instead of enclosing the data stream in a glass fiber, it is transmitted through the air. It is a secure, cost-effective alternative to other wireless connectivity options. Fig : A FSO Device History The engineering maturity of Free Space Optics (FSO) is often underestimated, due to a misunderstanding of how long Free Space Optics (FSO) systems have been under development. Historically, Free Space Optics (FSO) or optical wireless communications was first demonstrated by Alexander Graham Bell in the late nineteenth century (prior to his demonstration of the telephone!). Bell’s Free Space Optics (FSO) experiment converted voice sounds into telephone signals and transmitted them between receivers through free air space along a beam of light for a distance of some 600 feet. Calling his experimental device the “photophone,” Bell considered this optical technology – and not the telephone – his preeminent invention because it did not require wires for transmission. Free Space Optics (FSO) Although Bell’s photophone never became a commercial reality, it demonstrated the basic principle of optical communications. Essentially all of the engineering of today’s Free Space Optics (FSO) or free space optical communications systems was done over the past 40 years or so, mostly for defense applications. By addressing the principal engineering challenges of FSO, this aerospace/defense activity established a strong foundation upon which today’s commercial laser-based FSO systems are based. 1880 - Photophone Transmitter 1880 - Photophone Receiver Thus Alexander Graham Bell called his invention the "Photophone" and considered it his greatest invention. WORKING PRINCIPLE OF FSO Free Space Optics (FSO) transmits invisible, eye-safe light beams from one "telescope" to another using low power infrared lasers in the teraHertz spectrum. The beams of light in Free Space Optics (FSO) systems are transmitted by laser light focused on highly sensitive photon detector receivers. These receivers are telescopic lenses able to collect the photon stream and transmit digital data containing a mix of Internet messages, video images, radio signals or computer files.Commercially available systems offer capacities in the range of 100 Mbps to 2.5 Gbps, and demonstration systems report data rates as high as 160 Gbps. Free Space Optics (FSO) systems can function over distances of several kilometers. As long as there is a clear line of sight between the source and the destination, and enough transmitter power, Free Space Optics (FSO) communication is possible. Free-space optics (FSO) systems could be a viable option for many applications. They can be installed along any line of sight up to a little more than a mile. FSO systems are based on transceivers that include one or more laser diode transmitters and a corresponding receiver in a housing that also includes optical lenses, data processors, fiber connections and an alignment system. The technology is protocol-independent and can be used with ATM, SONET, Gigabit Ethernet or virtually any network. FSO systems commonly support data rates of 1.25G bit/sec, and systems up to 160G bit/sec are being developed. Transceivers can be located on a rooftop, on a corner of a building or indoors behind a Free Space Optics (FSO) window. Link lengths, or the distances between transceivers, are determined for site-specific weather conditions and can vary from more than 600 feet up to about a mile in a clear, dry atmosphere. FSO networks are based on either 780-nm to 850-nm or 1,550-nm laser wavelength systems, which have very different power and distance characteristics. Lasers of much higher power can safely by used with 1,550-nm systems than with 780-to-850-nm systems. This is because wavelengths less than about 1,400 nm are focused by the cornea into a concen-trated spot falling on the retina, which can cause damage. FSO operates in an unregulated section of the spectrum, so no permits are required by the Federal Communications Commission. Because there's no need to dig trenches to lay cable, the permits associated with digging up streets, disrupting traffic and the like also are eliminated, and installation normally is complete in a few days. FSO: Wireless, at the Speed of Light Unlike radio and microwave systems, Free Space Optics (FSO) is an optical technology and no spectrum licensing or frequency coordination with other users is required, interference from or to other systems or equipment is not a concern, and the point-to-point laser signal is extremely difficult to Free Space Optics (FSO) intercept, and therefore secure. Data rates comparable to optical fiber transmission can be carried by Free Space Optics (FSO) systems with very low error rates, while the extremely narrow laser beam widths ensure that there is almost no practical limit to the number of separate Free Space Optics (FSO) links that can be installed in a given location. How Free Space Optics (FSO) can help us FSO’s freedom from licensing and regulation translates into ease, speed and low cost of deployment. Since Free Space Optics (FSO) transceivers can transmit and receive through windows, it is possible to mount Free Space Optics (FSO) systems inside buildings, reducing the need to compete for roof space, simplifying wiring and cabling, and permitting Free Space Optics (FSO) equipment to operate in a very favorable environment. The only essential requirement for Free Space Optics (FSO) or optical wireless transmission is line of sight between the two ends of the link. For Metro Area Network (MAN) providers the last mile or even feet can be the most daunting. Free Space Optics (FSO) networks can close this gap and allow new customers access to high-speed MAN’s. Providers also can take advantage of the reduced risk of installing an Free Space Optics (FSO) network which can later be redeployed. Advantages of Free Space Optics (FSO) : Free space optical (FSO) systems offers a flexible networking solution that delivers on the promise of broadband. Only free space optics or Free Space Optics (FSO) provides the essential combination of qualities required to bring the traffic to the optical fiber backbone – virtually unlimited bandwidth, low cost, ease and speed of deployment. Freedom from licensing and regulation translates into ease, speed and low cost of deployment. Since Free Space Optics (FSO) optical wireless transceivers can transmit and receive through windows, it is possible to mount Free Space Optics (FSO) systems inside buildings, reducing the need to compete for roof space, simplifying wiring and cabling, and permitting the equipment to operate in a very favorable environment. The only essential for Free Space Optics (FSO) is Free Space Optics (FSO) line of sight between the two ends of the link. Free Space Optics (FSO) Security The common perception of wireless is that it offers less security than wireline connections. In fact, Free Space Optics (FSO) is far more secure than RF or other wireless-based transmission technologies for several reasons: Free Space Optics (FSO) laser beams cannot be detected with spectrum analyzers or RF meters Free Space Optics (FSO) laser transmissions are optical and travel along a line of sight path that cannot be intercepted easily. It requires a matching Free Space Optics (FSO) transceiver carefully aligned to complete the transmission. Interception is very difficult and extremely unlikely The laser beams generated by Free Space Optics (FSO) systems are narrow and invisible, making them harder to find and even harder to intercept and crack Data can be transmitted over an encrypted connection adding to the degree of security available in Free Space Optics (FSO) network transmissions. Wireless communicate from one point to another point High bit rate (10 Mbps to 2.5 Gbps) Set up a link in a few days The lasers used are eye safe, so even a butterfly can fly unscathed through a beam Military Application of FSO Air Force Its potential for low electromagnetic emanation when transferring sensitive data Navy Secure communication with submerged submarines. FSO vs RF RF 2.4 GHz systems were typically running at 2-4 Mbps due to interference issues in the unlicensed frequency ranges FSO provided 10 Mbps of throughput for less than unlicensed RF FSO was less cost, more secure, and seemed simpler Free Space Optics (FSO) Reliability of the FSO link To increase the reliability of an FSO link, two important methods have been proposed in the literature Hybrid Approach: Provide hybrid link protection using an RF link  Multi-hop approach: Scaling the hop length down between the transmitter and receiver using multi-hop routing. Challenge of FSO Challenge #1 — FOG Challenge #2—hitting the target Challenge #3—interrupted signals #1 FOG The primary challenge to FSO-based communications is dense fog. Rain and snow have little effect on FSO technology, but fog is different. Fog is vapor composed of water droplets, which are only a few hundred microns in diameter but can modify light characteristics or completely hinder the passage of light through a combination of absorption, scattering, and reflection Solution The primary answer to counter fog when deploying FSO-based optical wireless products is through a network design that shortens FSO link distances and adds network redundancies. FSO installations in extremely foggy cities such as San Francisco have successfully achieved carrier-class reliability #2 Hitting the target Getting a laser beam to hit the mark in a laboratory setting is easy, but in the real world it is much harder. Solution By using Active beam steering we can over come this challange. #3Interrupted signals An email is beaming across the FSO connection just as a bird flies through, blocking the signal. Solution Free Space Optics (FSO) No fear. FSO linkheads essentially "talk" to one another, and just as people repeat words in conversation, data can be retransmitted in the event of a temporary beam blockage. Several companies even have redundant radio-frequency links that simultaneously transmit the FSO signal. When the radio or the FSO signal is blocked, the counterpart is automatically used— no loss of data, and no delay. Companies and rapidly advancing FSO technology AirFiber: Hybrid Free- space optic/Radio .AirFiber's products combine FSO with 60 GHz millimeter-wave radio, makes wireless communication possible in any weather. ` LightPointe Multi-beam sending processLightPointe's FSO products utilize a multi-beam sending process, which overcomes atmospheric degradations and temporary beam obstructions by overlapping redundant infrared beams. Terabeam Carrier-grade FSO equipment and services.Terabeam's FSO products have advanced beam-steering features that update beam direction up to 300 times per second. Free Space Optics (FSO) General Applications: Typically scenarios for use are: * LAN-to-LAN connections on campuses at Fast Ethernet or Gigabit Ethernet speeds. *Connectivity Solutions *'Last-Mile' Network Solutions * LAN-to-LAN connections in a city. example, Metropolitan area network. * To cross a public road or other barriers which the sender and receiver do not own. * Speedy service delivery of high bandwidth access to fiber networks. * Converged Voice-Data-Connection. * Temporary network installation (for events or other purposes). * Reestablish high-speed connection quickly (disaster recovery). * As an alternative or upgrade add-on to existing wireless technologies. * As a safety add-on for important fiber connections (redundancy). * For communications between spacecraft, including elements of a satellite constellation Fig:- Two solar-powered satellites communicating optically in space via lasers. Free Space Optics (FSO) The light beam can be very narrow, which makes FSO hard to intercept, improving security. In any case, it is comparatively easy to encrypt any data traveling across the FSO connection for additional security. FSO provides vastly improved EMI behavior using light instead of microwaves. Conclusion The massive unregulated bandwidth of the optical channel makes optical wireless a potentially attractive solution to both providing wireless communications and augmenting RF wireless bandwidth.FSO is just starting to be applied to solve the Internet “last-mile” interconnectivity problem. Some believe that it may be the unlimited bandwidth solution for the metro urban core of downtown building-to-building communication, as well as the optimal technology for home-to-home and office-to-office connectivity. References: http://www.ieee.org/organizations/pubs/newsletters/leos/dec04/university.html Free Space Optics (FSO) http://www.lightpointe.com/ http://www.freespaceoptic.com/ http://www.fsonews.com/ http://www.cablefreesolutions.com/ http://www.thefoa.org/ http://www.free-space-optics.org/ http://www.freespaceoptics.com/ http://www.opticsreport.com/ Space Division Multiplexing,” presented at Free Space Laser Communications IV, Denver, 2004. oo, G. E. Faulkner, and D. C. O’Brien, “Novel system for the imaging of optical multipaths,” in Proc.SPIE 5210, pp. 47-54, 2003. J. Bellon, M. J. Sibley, V. A. Lalithambika, V. M. Joyner, R. J. Samsudin, D. M. Holburn, and R. J. Mears, “High-speed integrated transceivers for optical wireless,” IEEE-Communications-Magazine, vol. 41, pp. 58-62, 2003.
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